This invention relates generally to narrow band notch reflectors. More particularly, this invention relates to holographic notch reflectors in the near infrared range. Notch reflectors of this invention are extremely well suited for use in laser protective applications.
Holographic media are often utilized in narrow band notch reflectors. There is a perceived need for such narrow band notch reflectors in the near infrared (NIR) range, particularly for use in laser protection. Unfortunately, most holographic media are not sensitive to light in the NIR range. Dichromated gelatin holograms have been made to operate in the NIR by swelling the medium to increase the grating period, but it is difficult to stabilize the resultant holograms. Flat IR holograms have been created by exposing the medium at an oblique angle and thus increasing the grating spacing. However, this method is not applicable to holograms on curved substrates which are often required for laser protection applications. Representative examples of holographic narrow band notch reflectors indicative of the state-of-the-art are described in U.S. Pat. Nos. 4,830,441, 4,802,719, 4,786,125, 4,601,533 and 4,637,678. Many of these prior art methods require complex and undesired processing procedures associated with stacking multiple layers of film.